The present invention relates to an atomizer foil for atomizing a liquid in an air flow passing by the atomizer foil as this is located in a flow duct for the air flow, which atomizer foil is approximately shaped as an airfoil with two airfoil broad sides connected at a leading and a rear side edge as seen in the direction of air flow, and an inner duct intended for conveying the liquid and having an outlet at a leading part of the atomizer foil.
The invention also relates to an atomizer containing such an atomizer foil.
Finally, the invention relates to the use of such atomizer foil and/or the atomizer.
Atomizers of the kind mentioned in the introduction are known. An example of such an atomizer is known, for example, from the description to WO 87/00078. Even though an atomizer of this kind has shown an improvement in relation to previously known atomizers, it has appeared in practise that they give an uneven distribution of the liquid in the air flow. In practical tests it has thus shown that by using the atomizer, for example for dosing pesticides or herbicides, an uneven distribution of the liquid in the sprayed area has occurred. Thus there may occur overdosing in certain areas while other areas are underdosed with the desired liquid.
The atomizer foil will preferably be used in an atomizer mounted on a spraying boom together with a row of corresponding atomizers. The spray boom may be used for a field sprayer or the like. The sprayer may be suspended, towed, self-propelled, or a hand-held sprayer.
The sprayer may be placed in a sprayer housing which is a separate part of a spray boom, or which is an integral part of an spray boom.
The mixed flow media, air and liquid, will leave the atomizer in an approximately cone-shaped cloud. It is the distribution of the liquid in this xe2x80x9cair conexe2x80x9d which has appeared to be more uneven in the known constructions. Thus, it has appeared that the liquid drops do not occur with an even distribution or a normal distribution under the atomizer or with a high coefficient of variation.
It is the object of the present invention to indicate an atomizer and an atomizing foil that may give a usable distribution, either in the form of an even distribution or a normal distribution with limited coefficient of variation of the liquid under the atomizer.
This is achieved according to the present invention with an atomizer foil which is peculiar in that the inner duct comprises an inlet chamber connected with one or more outlet ducts, each extending in the longitudinal direction of the atomizer foil and having outlet on the leading side edge so that the outlet is disposed symmetrically in relation to a median plane through the width of the atomizer foil, and that the two airfoil broad sides are disposed symmetrically about said median plane.
The atomizer which makes possible the fulfilment of this purpose is according to the invention peculiar in that the used atomizer foil is provided as defined above and that the flow duct has an uniform section over a central part of its length.
The two flow media, air and liquid, are carried into an atomizer housing containing the atomizer foil. The air is guided through the flow duct of the atomizer housing, the duct may be rectangular or circular and passing the atomizer foil. The liquid is conveyed into the flow duct via the inner channel in the atomizer foil. The inner channel has an outlet at the leading part of the atomizer foil. In the present application, by the leading part of the atomizer foil there is meant that part of the atomizer foil facing the air flow passing through the flow channel. The liquid will thus be pressed/pumped out on the upper side of the two airfoil broad sides of the atomizer foil and will leave the atomizer foil at the rear part thereof. The liquid leaves the atomizer foil as small drops or atomized depending on the speed of the air flow.
By having a uniform flow duct and by arranging the atomizer foil with an inlet chamber connected to the outlet ducts having outlets on the leading side edge, it becomes possible to discharge liquid on the atomizer foil in a direction in parallel with the air flow through the flow duct. As the outlet ducts are disposed symmetrically in relation the median plane through the width of the atomizer foil, the same amount of liquid will be distributed on the two airfoil broad sides. By arranging the outlet symmetrically in relation to the length of the leading side edge, one may achieve an evenly distributed or normally distributed spreading of the liquid under the atomizer. This may be achieved irrespective of there is supplied a greater or lesser amount of liquid.
It is possible to use one or more outlet ducts. In practice, it is possible to use between 2 and 5 and preferably between 2 and 3 outlet ducts each having an opening disposed symmetrically in relation to the length of the leading side edge of the atomizer foil. That means the side edge facing the air flow.
The atomizer foil is disposed in the flow duct in parallel with the direction of the air flow which causes that an even air flow occurs over the two airfoil broad sides. Because of the uniform section of the flow duct, a uniform gripping force will occur along the width of the atomizer foil.
Practical tests have shown that there is achieved a well defined distribution of liquid with an atomizer foil that is designed in accordance with the invention.
It is possible to form the inlet chamber and the outlet ducts in different ways. The inlet chamber may have any angular, curved, or circular section. It is important that the outlet ducts extending from the inlet chamber extend perpendicularly to the inlet chamber and have a smaller sectional dimension than the inlet chamber. Hereby all of the inlet chamber will be filled with liquid and the liquid will be forced out through the outlet in a direction in parallel with the air flow. This forcing out of the liquid will be evenly distributed over all the outlet ducts if the outlet ducts have a smaller section than the inlet chamber. Hereby it is avoided that a larger amount of liquid will flow out of the outlet duct being closest to the inlet opening of the inlet chamber, the inlet opening usually being placed in one of the side walls of the atomizer foil.
Even though different dimensions and shapes are possible, it is preferred to utilise circular outlet ducts and inlet chambers for manufacturing reasons. The diameter of each outlet duct is preferably less than xc2xe of the diameter of the inlet chamber and will especially be lesser than half of said diameter. Furthermore, the outlet duct will have a length that at least correspond to the diameter of the inlet chamber and that the length of the outlet duct preferably will be at least two times the said diameter.
The two airfoil broad sides of the atomizer foil may curve over their width. However, it is advantageous that the airfoil broad sides have a rectilinear extension over all their width with an arbitrary point along the length of the airfoil broad sides. In other words, this means that there will be a uniform section over all the width of the atomizer foil. Hereby, there is achieved a uniform distribution of liquid over all the width of the atomizer foil and thereby a well-defined even distribution of the liquid under the atomizer.
In order to achieve a symmetrical flow condition and thereby an even and usable distribution of liquid, it is preferred that the leading and rear side edge of the atomizer foil extend in parallel and perpendicularly to the longitudinal direction of the atomizer foil. This means at the same time that the leading and the rear side edge extend perpendicularly to the air flow through the flow duct.
Furthermore, it is preferred that the rear side edge is a plane surface extending perpendicularly to the media plane through the atomizer foil. It has shown that such a plane surface gives a better distribution than a sharp edged side edge. Alternatively, it will also be possible to have a lesser rounding of the corners at the rear side edge.
The leading side edge of the atomizer foil will have a rounded shape corresponding to that which is known from wings of airplanes and thus also as it is seen from the accompanying drawing.
Alternatively, the leading side edge may be pointed as it also appears from the accompanying drawing.
However, it is important how the rear side edge of the atomizer foil is finished. The plane surface may be established directly in connection to the broad sides. However, there may also be formed a stepwise reduction so that a sectional reduction occurs at the rear part in connection with the rear side edge. Surprisingly it appears that a stepwise reduction from the broad sides with a flat rear side edge on the stepwise reduced part gives a very even distribution of drops in the formed cloud.
Furthermore, it appears to be important to make the atomizer foil with a marked curvature as compared to a more slender shape. In flow ducts with a rectangular section, the thickest part of the atomizer foil should be made so that it fills out much of the width in the flow duct of the atomizer housing. Thus it is preferred that the atomizer foil fills up at least half of the width of the atomizer duct at the point where the atomizer foil has its greatest thickness.
It has also appeared to be advantageous to use the atomizer foil with an orientation which is different than previously. Until now it has been assumed that the atomizer foil is placed in a boom with an orientation transverse to the direction of movement. However, surprisingly it has appeared to be advantageous if the atomizer foil is orientated in parallel with the direction of movement.
However, in this situation it is important to ensure the exact orientation of the atomizer foil with a median plane of the atomizer foil in parallel with a plane for a longitudinal section through the atomizer housing. This may be achieved by providing the longitudinal edges of the atomizer foil with guide means co-operating with guide grooves which are located in the wall of the flow duct. Hereby, there is achieved a secure control of the orientation of the atomizer foil and thereby a uniform spreading of the cloud being discharged from the atomizer.
By orientating the atomizer foil in parallel with the direction of driving, it has appeared to be possible to produce a cloud where the outermost part of the cloud may be brought to overlap a cloud formed by an adjacent atomizer. This is advantageous as one may hereby compensate for the reduced amount of drops which will be in peripheral area of the so-called douche area covered by the cloud from an atomizer.
The atomizer foil may be produced in different ways and of different materials depending on the intended use. However, it is suitable to make the atomizer foil by injection moulding of plastic.
An atomizer foil according to the invention will, because of a very even distribution of liquid gripped in the air flow, be suitable for use in an atomizer for dosing herbicides, pesticides or fertilisers. Alternatively, it will also be possible to use the atomizer foil in an atomizer used for dosing liquid nutrients.